7.3: Implement the Program

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Based on the algorithm, the following program can be created.

program period
! Program to calculate the period of a pendulum

! declare variables
!     real constants -> gravity, pi
!     reals -> angle, length, alpha
implicit none
real :: angle, length, pperiod, alpha
real, parameter :: gravity=980.0, pi=3.14159

! display initial header
    write (*,*) "Pendulum Period Calculation Program"
    write (*,*)

! prompt for and read the length and angle values
    write (*,*) "Enter Length and Angle values:"
    read (*,*) length, angle

! convert degrees to radians
    alpha = angle * pi / 180.0

! calculate the period
    pperiod = 2.0 * pi * sqrt(length/gravity) * &
        ( 1.0 + 1.0/4.0 * sin(alpha/2.0)**2 )

! display the results
    write (*,*) "The period is:", pperiod

end program period

The indentation is not required, but helps make the program easier to read. Note that the “2”, “1”, and “4” in the algorithm are entered as 2.0, 1.0, and 4.0 to ensure consistent data typing (i.e., all reals). When 1 divided by 4 is entered as “1/4” instead of “1.0/4.0” the result will be 0 because that would be integer division.